Synthesis of Novel Alicyclic Poly(thioether sulfone) with High Refractive Index and High Abbe’s Number Using 1,4-Dithiin 1,1-Dioxide

A novel alicyclic 1,4-dithiin (DT)-based poly(thioether sulfone) (PTES) was successfully synthesized through the polyaddition reaction of 2,5-bis(sulfanylmethyl)-1,4-dithiane (BMMD) with 1,4-dithiin 1,1-dioxide (DTDO). This is the first study to synthesize and identify DTDO with a boat-shaped conformation, as confirmed by nuclear magnetic resonance spectroscopy and X-ray crystallography. It was found that, in a model reaction, benzyl mercaptan (BM) and novel compound, DTDO, underwent the typical Michael-type addition reaction in the presence of a base. Based on this result, the Michael polyaddition reaction between BMMD and DTDO was performed in the presence of N,N-diisopropylethylamine in N-methyl-2-pyrrolidone. As a result, a high-molar-mass PTES, Poly(BMMD/DTDO) (Mw up to 23,900 g/mol), was successfully obtained. Poly(BMMD/DTDO) features high thermal stability as an aliphatic polymer, exhibiting a 5% weight loss temperature (Td5%) of 278 °C and a high glass transition temperature (Tg) of 131 °C. The Poly(BMMD/DTDO) film exhibited excellent optical properties, including high transparency (T% = 94.7%@450 nm), average refractive index (nav = 1.6719@594 nm), and Abbe’s numbers (νdTE/νdTM = 37.8/37.6), as predicted by density functional theory calculations. Furthermore, the Poly(BMMD/DTDO) film consists of highly isotropic amorphous phases, exhibiting a small birefringence (Δn = −0.0002). The high proportion of alicyclic structures and sulfur content (53.3 wt %), as well as the incorporation of SO2 units into the polymer, represent a promising molecular design strategy for producing PTESs with excellent thermal and optical properties that are suitable for optical lens materials.